(726a) Modeling Combinatorial Insulin Secretion Dynamics of Recombinant Hepatic and Intestinal Cells

Combination cell therapy entails the use of more than one cell type in providing improved functional replacement of a diseased tissue or organ. Use of combination of cells is a more realistic representation of natural tissue and an increasing amount of evidence points to their synergistic effect (Bonaroas et al., 2007). With combined cell therapy it is possible to enhance the efficacy by merging the beneficial effects of each of the cell type. One of the most promising cell-based therapies for combating insulin-dependent diabetes entails the use of genetically engineered non- β cells that secrete insulin in a glucose-responsive fashion. A normal pancreatic β cell secretes insulin in a biphasic manner. The first phase is characterized by a transient stimulation of insulin to rapidly lower the blood glucose levels which is followed by a second phase of insulin secretion to sustain the lowered blood glucose levels over a long period of time. Due to different insulin secretion kinetics in recombinant enteroendocrine and hepatic cells, we hypothesized that a combination of hepatic cells and enteroendocrine cells will be more efficacious in achieving normoglycemia by mimicking the biphasic insulin secretion of normal β cells. This work focuses on developing a quantitative mathematical model of each of the recombinant cells and to design a combined system that exhibits optimal insulin secretion kinetics. Insulin secretion experiments were conducted with two hepatic cell lines (HepG2 and H4IIE) transduced with adenoviral constructs expressing insulin along with a stably transfected recombinant intestinal cell line (GLUTag-INS). It was found that the recombinant hepatic cells secreted insulin in a more sustained manner where as the recombinant intestinal cell line exhibited rapid insulin secretion kinetics upon stimulation. These secretion data was incorporated into the mathematical model which takes into account insulin cDNA transcription, mRNA translation, proinsulin processing, and tracks the concentration of pro-insulin and insulin through various intracellular compartments and into the extracellular medium. Due to the different locales of these recombinant cells in vivo, the combinatorial kinetics was assumed to be addition of the two insulin secretion profiles without any interaction effects. The model helps evaluate the relative cell numbers required of each recombinant cell type to simulate the bi-phasic insulin secretion kinetics to achieve normoglycemia. Future work includes refining the model on the basis of measured insulin secretion dynamics in vitro to increase its accuracy. The model provides the basic framework in understanding the secretion kinetics of the combined system and takes it a step closer towards its in vivo implementation.